July 20, 2011

An overview of open-source 3d printer technologies

I’ve been building a reprap 3d printer, and that’s got me interested in 3d printing in general. I decided to do a quick overview of the different technologies and link to an open-source project working on that type of technology.

What is 3d printing?

3d printing is the idea of making a physical object by combining layers of material together. Think of it like the calculus concept of integration — you put down layer after layer of material, so thin that each layer is basically a drawing — but over time, get something real and large. Like making a book from pages, you build a model from plastic/powder/other material.

Sintering

Sintering is a method of 3d printing where a powder material is fused together by heat, glue, or both. This is also known as powder printing. The idea is that you have a “sheet” of powder that you then stinter together into a shape, then stinter the layers together into a model. The adderfab project at the university of washington is probably the best known of the open-source projects using this technology. A well known commercial entity using sintering is Z-Corp. this technology is messy — you get powder everywhere, and tends to produce very weak parts. I’ve broken models just by touching them, or removing them from a printer! But, this technique has good resolution and makes excellent molds. Many people use this technique to create glass or ceramic parts by printing a mold first, then pouring in a glass/ceramic, then heating.

Another project in the Sintering world is AndreasBastion’s 3d printer. It uses an IR diode to harden a powder of wax and carbon, and can be used to make positives for sand-casting/lost casting.

Known materials

When using sintering, three classes of materials are known to work well. The first is dry plaster/cement powders or their components( like sand ), the second class are ceramic powders like clay, and the third are metal powder mixes. The adderfab folks are using hydroperm plaster with rice wine/vinegar as a glue, there are reports of people sintering sand using sunlight and a powerful lens in the desert, and lastly, there are publications advocating the use of Nylon-12 coated aluminum with a CO2 laser in an inert atmostphere.

Fused filament/deposition modeling

Abbreviated FFM or FDM, this technology takes a thin wire, usually plastic, and melts it into a semi-liquid state. It then deposits the gelled plastic onto a layer, and the plastic is sticky enough to attach layers together. The RepRap project and its commercial spinoffs — such as Makertbot, or Bits From Bytes are the most commonly heard of projects in this space. This process produces stronger parts, but the parts are heat sensitive and have low resolution compared to the other methods. The heat sensitivity prevents working in glass or ceramics using this method. The low resolution makes commercial work difficult. However, this method is well documented, cheap, and easy to get into versus the other methods at this time.

Liquid Deposition Modeling

Many people would lump this in with FFM/FDM — but I view it differently. Liquid deposition modeling does not melt a starting material, but rather, starts with a liquid/gel material. Examples include silicon, silly putty, food, etc.. The Fab@home project is probably the best known of this type, though reprap derived printers can also use this method. This method has the same low resolution of FFM/FDM, limited by the accuracy of the stepper motors used to drive the print head and the size of the print aperture. However, since the materials here start as liquids and dry to their final state, it can print in materials that can be thermally stable, like silicone or caulk. This allows it to be used in mold making. Some of these printers have multiple print heads, and can print in more than 1 material at a time, allowing for different colored products or other benefits.

Lithographic printing

In this methods, a layer of resin is hardened by a laser, LED, or other light source. The process is photochemical in nature, and can take advantage of the fact that we humans know how to control light well and with speed and precision. This method is fast and has very high resolution. It also uses toxic chemicals and is perhaps a little dangerous to use in a home setting. The current resins tend to depolymerize over time, resulting in models that “melt” over time. However, in terms of speed and accuracy, this method is perhaps the best method to get good-looking parts. I know of two projects in this space — neither one of them open source or available yet to the general public The Micro Printer at Vienna University of Technology, and Junior’s home-made printer.

–Updates, March 2012–

Junior’s Project and the Micro printer seem to have become the same thing, as Junior is implementing the ideas from the Micro-printer, and the two creators have joined forces.

There’s now 2 new projects in this space, and a few cheap UV cure resins available in the market.

Bucktown 385 cure resins — about $39.00/Quart. Please note, they have multiple offerings — I’ve just linked to their most basic. They are A CMYK resin system, so you can make almost any color you like, except clear.